Papers by Keyword: EPR

Abstract: Electron paramagnetic resonance (EPR) linewidth in the Cd1-xMnxS bulk crystals with manganese concentrations x = 0.25, 0.33, 0.35 and 0.42 has been studied in the high-temperature region. An analysis of the infinite-temperature EPR linewidth performed within the exchange narrowing model shows that the contributions of the anisotropic superexchange and magnetic dipolar interaction to the linewidth are nearly the same due to weak anion spin-orbit coupling. The single-ion anisotropy originating from the crystal field of axial symmetry with the parameter Dsingle= 0.0295 cm-1, as observed in some CdS:Mn crystals, gives a contribution to the linewidth comparable with the influence of the anisotropic superexchange and magnetic dipolar interaction. The calculated infinite-temperature linewidths, including all anisotropic spin interactions examined in this work, are close to the experimental infinite-temperature linewidths estimated from the existing high-temperature data.

Abstract: Electron paramagnetic resonance (EPR) was used to study 4H- and 6H-SiC doped with P during chemical vapour deposition (CVD) growth. In 6H-SiC, three spectra with C3v symmetry and spin S=1/2, labelled Ph, Pc1 and Pc2, were detected. The g-values and the 31P hyperfine (hf) constants were determined for Ph: g||=2.0046, g^=2.0028, and A||=0.103 mT, A^<0.05 mT; for Pc1: g||=2.0039, g^=2.0025, and A||=0.615 mT, A^=0.43 mT; for Pc2: g||=2.0038(5), g^=2.0025, and A||=0.40 mT, A^=0.22 mT. The hf interaction with nearest 13C neighbours were also observed for the Pc1 and Pc2 centers, confirming that in CVD grown material the shallow P donor occupies the Si site. The Ph, Pc1 and Pc2 centers are assigned to the ground states of the shallow P at the hexagonal (Ph) and quasi-cubic sites (Pc1 and Pc2) in 6H-SiC. In 4H-SiC, an EPR spectrum of C3v symmetry with a larger anisotropy in the g-values (g||=2.0065 and g^=2.0006) was observed. The temperature dependence of the spectrum is similar to that of Ph in the 6H polytype. Its 31P hyperfine constants are determined as A||=0.294 mT and A^=0.21 mT.

Abstract: The conclusion which is drawn from the EPR line broadening and narrowing of the N shallow donor in an isotope enriched and non-enriched 4H-SiC and 6H-SiC crystals along with previous ENDOR results shows that the spin-density distribution over the C and Si nuclei differs between the 4H-SiC and 6H-SiC polytypes. The main part of the spin density in 4H-SiC is located on the Si sublattice. In contrast, in 6H-SiC the main part of the spin density is located on the C sublattice. An explanation for the difference in the electronic wave function of the N donor in 4HSiC and 6H-SiC can be found in the large difference in the band structure of two polytypes and in the position of the minima in the Brillouin zone.

Abstract: The high-temperature stable defect complexes in 6H-SiC crystals created by heavy neutron irradiation and following high-temperature annealing have been discovered by EPR. After annealing at 1500°C at least five new axially symmetric centers with the electron spin S = 1/2 and S = 1 were shown to arise in 6H-SiC crystals. The striking feature of all discovered centers is a strong hyperfine interaction with a great number (up to twelve) of equivalent host Si (C) atoms. Two models, a four-vacancy complex VSi-3VC, and a split-interstitial antisite (C2)Si or a pair of two antisites (C2)Si-SiC are discussed. There is a good probability that some of new centers could be related to the famous D1 and DII centers. After annealing at 2000°C the dc1-dc4 centers disappeared and a new triplet center labeled as N-V in the form of a silicon vacancy and a nitrogen atom in neighboring carbon substitutional position has been observed. The parameters of this center are similar to that for well-known N-V center in diamond.

Abstract: We identify the VSiCSi(SiCCSi) complex in electron-irradiated 6H-SiC samples. Based on the analysis of new photo-excited EPR spectra, and supported by theoretical calculations, it was possible to establish its microscopic structure and to conclude that this complex is formed from the first product of the Si-vacancy annealing, the VSiCSi complex (also known as P6/P7 centers).